Multiple .cpp files

I have 6 .cpp files, each containing Dialog procedures and some functions. I also connect to a SQLite database - I read location of database from config file and the main problem is...

How to store config value in main.cpp (first file) that will be simply accessable in other .cpp files ?

Thanks for all answers!

Would a global variable in a header file suffice? Or you could declare extern variables defined elsewhere in your program.

OK, I tried to put a variable in header, which is included by all .cpp files, and I got this error from linker:

Quote:

---

make -f Makefile.win
g++.exe obj/functions.o obj/main.o obj/login.o obj/users.o obj/groups.o obj/cars
.o obj/profile.o obj/nalogi_private.res -o "bin\nalogi.exe" -L"D:/Emil/devcpp/li
b" -L"D:/Emil/devcpp/dokumenti/nalogi/headers" -L"D:/Emil/devcpp/dokumenti/nalog
i" -mwindows ../../lib/libsqlite3.a static/md5.a ../../lib/libsqlite3_plus.a sta
tic/CppSQLite3.a lib/sqlite3.lib -lgmon -pg -fmessage-length=0
obj/main.o:main.cpp:(.bss+0x0): multiple definition of `user'
obj/functions.o:functions.cpp:(.bss+0x0): first defined here
obj/main.o:main.cpp:(.bss+0x20): multiple definition of `md5'
obj/functions.o:functions.cpp:(.bss+0x20): first defined here
obj/main.o:main.cpp:(.bss+0x5c): multiple definition of `db'
.......

---

Anybody?

why not use a class and a static variable? or you could even just pass the instance of the class around...

the same way you'd pass around any other variable... here's an example of using a class with a static member:

main.cpp

Code:

---

#include <iostream>
#include "test.h"
#include "test1.h"

int main()
{
        testClass a;
        a.writeVal(10);
        std::cout<<a.readVal()<<std::endl;
        changeVal(0);
        std::cout<<a.readVal()<<std::endl;
        return 0;
}

---

test.h:

Code:

---

#ifndef __TEST_CLASS__
#define __TEST_CLASS__

class testClass
{
        public:
                testClass(const int in=0);
                void writeVal(const int in);
                int readVal();
        private:       
                static int val;
};

int testClass::val=0;
testClass::testClass(const int in)
{
        val=in;
}
void testClass::writeVal(const int in)
{
        val=in;
}
int testClass::readVal()
{
        return val;
}

#endif

---

test1.h:

Code:

---

#ifndef __TEST_FUNCTION_H__
#define __TEST_FUNCTION_H__

#include "test.h"

void changeVal(const int in)
{
        testClass a(in);
}

#endif

---

now here's how you would pass an instance of the class (I wouldn't use this in your case)

main.cpp:

Code:

---

#include <iostream>
#include "test.h"
#include "test1.h"

int main()
{
        testClass a;
        a.writeVal(10);
        std::cout<<a.readVal()<<std::endl;
        changeVal(0,a);        //passing in class a by reference
        std::cout<<a.readVal()<<std::endl;
        return 0;
}

---

test.h:

Code:

---

#ifndef __TEST_CLASS__
#define __TEST_CLASS__

class testClass
{
        public:
                testClass(const int in=0);
                void writeVal(const int in);
                int readVal();
        private:       
                int val;        //this no longer needs to be static
};

//int testClass::val=0;
//this is no longer needed because it's not static
testClass::testClass(const int in)
{
        val=in;
}
void testClass::writeVal(const int in)
{
        val=in;
}
int testClass::readVal()
{
        return val;
}

#endif

---

test1.h:

Code:

---

#ifndef __TEST_FUNCTION_H__
#define __TEST_FUNCTION_H__

#include "test.h"

//now that you have testClass a, you can use any of it's public methods
//        (readVal or writeVal in this case)
void changeVal(const int in,testClass&a)
{
        a.writeVal(in);
}

#endif

---

edit: there's no way I imagined that post... I could have sworn I saw him ask how to pass an instance of a class around...

OK. Sorry for deleting post, I thought that I will figure out myself, but I couldn't :(

Here's the class definition:

PHP Code:

---

class DataAll
{
private:
static const char* sqlite_path;
static CppSQLite3DB db;
static CMD5 md5;
static Uporabnik user;
 
public:
CppSQLite3DB GetDbConn();
CMD5 GetMD5();
const char* GetDbPath();
Uporabnik GetStructUporabnik();
bool WriteStructUporabnik(Uporabnik structure);
}; 


---

And the way how I use the class...:

PHP Code:

---

const char* DataAll::sqlite_path = "program.db";
DataAll Data;
CppSQLite3DB db = Data.GetDbConn();
const char* sqlite_path = Data.GetDbPath();
Uporabnik user = Data.GetStructUporabnik(); 


---

But I still get the same errors from linker (altough now are poiting to class variables)... :confused:

Quote:

---

Originally Posted by publikum

OK. Sorry for deleting post, I thought that I will figure out myself, but I couldn't :(

Here's the class definition:

...

And the way how I use the class...:

...

But I still get the same errors from linker (altough now are poiting to class variables)... :confused:

---

what errors are you getting? if they're errors about not undefined references, it's probably because you forgot to define your static data members (they have to be defined outside the class body - I.E. the declaration does not count as a definition, as opposed to a regular data member, where all you need to do is declare it in the class body.

Code:

---

class DataAll
{
        private:
                static const char* sqlite_path;
                static CppSQLite3DB db;
                static CMD5 md5;
                static Uporabnik user;

        public:
                CppSQLite3DB GetDbConn();
                CMD5 GetMD5();
                const char* GetDbPath();
                Uporabnik GetStructUporabnik();
                bool WriteStructUporabnik(Uporabnik structure);
};

/* this is the part I was talking about */
const char* DataAll::sqlite_path = "program.db";
CppSQLite3DB DataAll::db=???;
CMD5 DataAll::md5=???;
Uporabnik DataAll::user=???;

---

OK, thanks for solution, but I still get an error from linker:

Quote:

---

make -f Makefile.win
g++.exe obj/functions.o obj/main.o obj/login.o obj/users.o obj/groups.o obj/cars
.o obj/profile.o obj/nalogi_private.res -o "bin\nalogi.exe" -L"D:/Emil/devcpp/li
b" -L"D:/Emil/devcpp/dokumenti/nalogi/headers" -L"D:/Emil/devcpp/dokumenti/nalog
i" -mwindows ../../lib/libsqlite3.a static/md5.a ../../lib/libsqlite3_plus.a sta
tic/CppSQLite3.a lib/sqlite3.lib -lgmon -pg -fmessage-length=0
obj/main.o:main.cpp:(.bss+0x24): multiple definition of `DataAll::user'
obj/functions.o:functions.cpp:(.bss+0x0): first defined here
obj/main.o:main.cpp:(.bss+0x40): multiple definition of `DataAll::md5'
obj/functions.o:functions.cpp:(.bss+0x20): first defined here
obj/main.o:main.cpp:(.bss+0x7c): multiple definition of `DataAll::db'
obj/functions.o:functions.cpp:(.bss+0x5c): first defined here
........more errors like this........
collect2: ld returned 1 exit status
make: *** [bin/nalogi.exe] Error 1

---

For your case you'd probably just want to use global variables. Just stick it in a header file that's included in all the other ones and you can use it in all of them.

Remember, if you create your global int lalala, remember to get rid of the int lalala = ... in your files, I'm guessing that's what caused the multiple definition errors.

so what does your code look like so far?

I suggest NOT using global variables... ever.

Here's the code that I use in all .cpp files:

PHP Code:

---

const char* DataAll::sqlite_path = "program.db";
DataAll Data;
CppSQLite3DB db = Data.GetDbConn();
const char* sqlite_path = Data.GetDbPath();
Uporabnik user = Data.GetStructUporabnik(); 


---

what about the class declaration and it's definitions?

you are using the sqlite .dll?

from reading the api, the db location is a file in the application directory, unless you specify otherwise.

you could use a conditional definition of the include, so it's only actually included once.
that will get rid of the multiple definition errors.

If you have to use globals, you can group them in a class like this

Globals.h

Code:

---

#include <string>

class Globals
{
        public:
                static std::string Path;
                static int Value;
};

---

Globals.cpp:

Code:

---

#include "Globals.h"

std::string Globals::Path = "initialised";
int Globals::Value = 99;

---

main.cpp:

Code:

---

#include "Globals.h"

#include <string>
#include <iostream>

int main()
{
        std::cout << Globals::Path << std::endl;
        std::cout << Globals::Value << std::endl;


        Globals::Path = "c:\\test\\testfile.txt";
        Globals::Value = 7;

        std::cout << Globals::Path << std::endl;
        std::cout << Globals::Value << std::endl;

    return 0;
}

---

First, be sure you have used inclusion gaurds in all of your header files. See code posted by major_small for an example of the necessary syntax if you aren't familiar with it.

Then, trying to piece things together, in the class declaration for DataAll you declare sqlite_path and user to be static variables with these lines:

static const char* sqlite_path;
static Uporabnik user;

Then you say you do define sqlite_path in all cpp files

>Here's the code that I use in all .cpp files:

by doing this:

>const char* DataAll::sqlite_path = "program.db";

However, since DataAll::sqlite_path is a static variable, this amounts to multiple definition of sqlite_path, as that sort of statement should only be made once, usually in the header file where DataAll is declared. Again, see major_smalls code for an example. I don't see DataAll::sqlite_path listed in the series of error statements you have posted:

>I still get an error from linker:

and I don't see that you do the same sort of thing with DataAll::user as you do with DataAll::sqlite_path in the code you posted, though I do see the multiple definition error for DataAll::user

>multiple definition of `DataAll::user'

so I suspect that you are doing the same thing with DataAll::user, and the other static variables that are listed in the error statements posted, that you do with DataAll::sqlite_path and I suspect that there is a multiple definition error statement with DataAll::sqlite_path in it some place in the list of errors that didn't get posted.

If you want to use a DataAll object in several different cpp files then define the static variables just once, in DataAll.h, as per major_smalls example and include the DataAll.h header file in each file that uses the DataAll object. Then you can use the static variables as you would other variables of the object, again, see major_smalls code for an example.

Thanks guys, you're great! I read the whole thread 3 times and then I finally got up with a working idea!

Thanks again for all help and answers!!!